The two-term Mississippi governor and former chairman of the Republican National Committee cited a lack of passion for the presidential slugfest. "A candidate for president today is embracing a 10-year commitment to an all-consuming effort, to the virtual exclusion of all else," Barbour said in a statement. "His (or her) supporters expect and deserve no less than absolute fire in the belly from their candidate. I cannot offer that with certainty, and total certainty is required."

The former Arkansas governor, ordained Southern Baptist minister, winner of the 2008 Iowa caucuses and runner-up to John McCain in the ultimate delegate count that year announced on his Fox News Channel program that he wasn't running again. "All the factors say go, but my heart says no," Huckabee said. "And that's the decision that I have made."

The businessman/reality TV star declared that if he ran he'd win, but that he wouldn't run. "I have spent the past several months unofficially campaigning and recognize that running for public office cannot be done half heartedly," Trump said in a statement. "Ultimately, however, business is my greatest passion and I am not ready to leave the private sector."

The second-term Indiana governor, former political director for President Ronald Reagan and former budget director for President George W. Bush broke the news to supporters via email. "If you feel that this was a non-courageous or unpatriotic decision, I understand and will not attempt to persuade you otherwise. I only hope that you will accept my sincerity in the judgment I reached." Daniels told The Indianapolis Star that his wife and daughters had the final say. "Simply put, I find myself caught between two duties. I love my country; I love my family more."

The former two-term Minnesota governor became the first official candidate to leave the race, announcing his decision hours after a third-place finish in the Iowa straw poll. "There are a lot of other choices in the race," Pawlenty explained. "The audience, so to speak, was looking for something different."

The first-term New Jersey governor went so far as to make a late-September speech on "Real American Exceptionalism" at the Ronald Reagan Presidential Foundation & Library in Simi Valley, Calif. But a week later (and despite being implored by some Republican leaders to enter the race) Christie called a news conference at the New Jersey statehouse to decline. "Now is not my time. ... I have a commitment to New Jersey that I simply will not abandon."

The former Alaska governor and John McCain's running mate on the 2008 Republican ticket used conservative talk radio to make official what most observers already had figured out. "Not being a candidate, really you are unshackled and you're able to be even more active," Palin said on Mark Levin's radio show. "I need to be able to say what I want to say."

While denying allegations of sexual harassment and claims of an extramarital affair, the former Godfather's Pizza executive, former chairman of the Federal Reserve Bank of Kansas City, Mo., and conservative radio talk show host said "continued distractions" were forcing him from the race. Cain had been the surprise winner of September's Florida straw poll and gained attention for his simplified "9-9-9" tax plan.

The former two-term governor of New Mexico, who had been excluded from most of the Republican debates, announced he was leaving the GOP race to seek the Libertarian Party's nomination. At a debate where he was included, on Sept. 22 in Orlando, Fla., Johnson voiced one of the most memorable TV moments of the campaign season: "My, uh, next-door neighbor's two dogs have created more shovel-ready jobs than this current administration."

The day after a sixth-place finish in the Iowa caucuses, the Minnesota congresswoman left the race. "Last night, the people in Iowa spoke with a very clear voice, and so I have decided to step aside," Bachmann announced. Her candidacy reached a high point in August, when she won the Iowa Republican Party's straw poll. But that victory was blunted, and much of her Tea Party support diverted, that same weekend when Texas Gov. Rick Perry joined the race.

Six days after calling a third-place finish in the New Hampshire primary his "ticket to ride," the former Utah governor left the race and endorsed his fellow Mormon and longtime rival. "Today I am suspending my campaign for the presidency. I believe it is now time for our party to unite around the candidate best equipped to defeat Barack Obama. Despite our differences and space between us on some of the issues, I believe that candidate is Mitt Romney."

Under pressure from some conservatives to throw his dwindling support to Newt Gingrich in an effort to halt the Mitt Romney train, the Texas governor did just that two days before the South Carolina primary. Declaring "no viable path forward" for his own campaign, Perry said: "I know when it's time to make a strategic retreat."

After struggling to be taken seriously by the Republican establishment or get access to the all-important televised debates, the former Louisiana governor and member of Congress — and former Democrat — left the GOP race to seek the nomination of both the Americans Elect movement and the Reform Party.

With the delegate math stacked against him and his 3-year-old daughter in the hospital over Easter weekend, the former Pennsylvania senator huddled with his family at the kitchen table where his candidacy began and decided to end his White House bid. The campaign has been "miracle after miracle," he said in a speech in Gettysburg, Pa. "This race was as improbable as any race you'll ever see for president."

The junior senator from South Dakota became the first major figure to remove himself from contention after openly exploring a run for the presidency. "I feel that I am best positioned to fight for America's future here in the trenches of the United States Senate," Thune said in announcing his decision.